Chemistry Class-11: Chapter –1. Some Basic Concepts of Chemistry – Part-4

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III. Short Answer Type

Question-23:

What will be the mass of one atom of C-12 in grams?

Answer:

Question-24:

How many significant figures should be present in the answer of the following calculations?

Answer:

Question-25:

What is the symbol for SI unit of mole? How is the mole defined?

Answer:

Symbol for SI Unit of mole is mol.

One mole is defined as the amount of a substance that contains as many particles or entities as there are atoms in exactly of the isotope.

Question-26:

What is the difference between molality and molarity?

Answer:

Molality is the number of moles of solute present in one kilogram of solvent but molarity is the number of moles of solute dissolved in one litre of solution.

Molality is independent of temperature whereas molarity depends on temperature.

Question-27:

Calculate the mass percent of calcium, phosphorus and oxygen in calcium phosphate .

Answer:

Question-28:

of dinitrogen reacted with of dioxygen and of nitrous oxide was formed. The reaction is given below:

Which law is being obeyed in this experiment? Write the statement of the law?

Answer:

According to Gay Lussac’s law of gaseous volumes, gases combine or are produced in a chemical reaction in a simple ratio by volume, provided that all gases are at the same temperature and pressure.

Question-29:

If two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element, are in whole number ratio.

(a) Is this statement true?

(b) If yes, according to which law?

(c) Give one example related to this law.

Answer:

(a) Yes

(b) According to the law of multiple proportions

(c)

(c)

Here masses of oxygen, which combine with fixed mass of hydrogen are in the simple ratio i.e.,

Question-30:

Calculate the average atomic mass of hydrogen using the following data:

Isotope, Abundance and Molar Mass
Isotope, abundance and molar mass

Isotope

% Natural abundance

Molar mass

99.985

1

0.015

2

Answer:

Question-31:

Hydrogen gas is prepared in the laboratory by reacting dilute with granulated zinc. Following reaction takes place.

Calculate the volume of hydrogen gas liberated at STP when of zinc reacts with . of a gas occupies volume at STP; atomic mass of .

Answer:

From the equation, of zinc liberates litre of hydrogen. So will liberate